Carbon dioxide is a principal component of the metabolism of all vertebrate animals. Animals breath air. Oxygen in the air is captured in the lungs by hemoglobin in blood. Oxygenated blood is distributed to cells throughout the animal where it supplies key building-blocks to cells, and the oxygen is used to metabolize or“burn” carbon compounds, supplying energy required for cell processes. The carbon dioxide produced during this aerobic metabolism is then transported back to the lungs with deoxygenated blood and respired as carbon dioxide (and a few other gaseous waste products) in the animal's breath. In addition to lungs, ruminant animals have a digestive tract compartment called the rumen which harbors microbes that process grass in the absence of oxygen. This anaerobic fermentation produces large amounts of microbial protein. The end result is that ruminants are able to convert very low protein plant material into building blocks that are subsequently assimilated by the ruminant as the feed and microbial residue passes through the digestive tract.
Since the fermentation of forage material in the rumen is largely completed in the absence of oxygen, large amounts of methane and carbon dioxide are formed. These gases build-up in the rumen and create pressure that must be relieved. As a ruminant animal (such as a cow) exhales, the gaseous contents are forced from the rumen into the aesogophagus where it is exhaled (eructated—belched) preceeding an exhalation. These eructations or belches are not optional. For a well-fed animal they must occur approximately every forty seconds or the animal will bloat. Most of the gas produced in the rumen is eructated through the animal's nose. A small amount is dissolved in the blood and much of that is released through the lungs. The process is ecologically significant because it allows ruminant animals to utilize relatively-low-quality forage as food and to process it anaerobically, creating nutritious by-products and microbial protein that are used by the animal to produce high quality meat and milk. Ruminant gas fluxes are influenced by animal genetics, feed composition, consumption and behavior. As a result, changes in any of these parameters are likely to be quickly reflected in the fluxes of methane and carbon dioxide that are emitted in the course of the ruminant animal's breathing and eructations.
Routine measurements of ruminant methane and carbon dioxide emission fluxes and the fluxes of other metabolic gases, if possible and cost-effective, would provide very sensitive indicators to monitor and tune animal function. This would be much like using engine exhaust analysis to monitor performance and to tune fuel flow, combustion timing, and air mixtures to maintain optimal performance of a car engine. Changes in the fluxes of methane and carbon dioxide could inform management of optimal feed composition, the genetic feed efficiency of individual animals, and changes in animal health and behavior. In addition, methane emissions, although necessary, still represent a significant potential feed efficiency loss of roughly five to ten percent of the animal's gross energy intake. That equates to about one third to about one half a pound of lost potential weight gain per day. Therefore, changes in management that reduce methane fluxes can also potentially result in a net reduction of several dollars in feed costs per animal per day.
In modern, high-volume, low margin CAFOs (concentrated animal feeding operations), thousands of animals are housed and fed in very close quarters with a minimum labor force. Under these conditions, it is difficult or impossible to individually monitor the health of each animal. However, intensive observations and individualized monitoring can be economically important. For example, many diseases if not diagnosed and treated quickly can rapidly create epidemics within a confined herd. New equipment in modern dairies can be used to monitor milk production and other physical characteristics for each animal. However, by the time a problem is detected in the final products of an animal's metabolism, it is often too late to avert the loss of an individual or to prevent the spread of disease to others in the herd. Clearly, new technology is needed to effectively monitor each individual in large confined populations under crowded conditions.
Independent of disease monitoring, operator awareness of individual animal behavioral changes that are reflected in changes in grazing behaviour and animal activity can be economically important. For example, the research literature indicates that when an animal comes into heat (estrus) her grazing intake decreases and her general movement activity increases. These changes signal the optimal time for insemination of the animal to achieve pregnancy. These changes in behavior are thus also likely to be quickly reflected in methane fluxes and methane and carbon dioxide emission ratios. Similarly, changes in feed quality or composition that can occur when feed ingredients are modified or when cattle are moved to new pastures are likely to impact both the fluxes and the ratios of metabolic gas emissions.
In western feedlots, distiller's grain, which is a bi-product of methanol production from corn, is a preferred feed. However, ethanol plants often use sulfur-containing compounds to clean and disinfect plant facilities. Residue from these compounds can contaminate a distiller's grain. When feedlot cattle subsequently consume the grain, hydrogen sulfide is produced in the rumen. If not recognized immediately, the result often is the death of the animal. Routine monitoring of the animal's breath for hydrogen sulfide could, therefore, lead to early detection of contaminated feed and prevent large economic losses to the CAFO industry.
Individual monitoring to continually assess animal performance in rangelands can likewise be problematic. It is often difficult for producers and operators to assess the quality and quantity of available forage in pastures and to quantitatively determine changes in forage that occur as grazing progresses. The literature has documented that changes in forage quality are reflected in changes in methane and carbon dioxide fluxes from ruminants. Therefore, monitoring fluxes can potentially inform producers to maximize grazing effectiveness and to maintain sustainable productivity.
In rangelands, animals often are not easily approached and handled. In addition, grazing animals have evolved behavioral mechanisms to hide vulnerabilities from potential predators. Therefore, routine and comparative diagnostic observations of animals to assess health and performance are relatively difficult and expensive. Automated monitoring of metabolic gases could inform managers of changes in the health of individual animals. In some rangelands, toxic substances, such as some sulfur compounds, can accumulate in vegetation and water supplies. These substances can result in ruminant mortality. Hence, routine monitoring of specific metabolic gases, such as hydrogen sulfide, that are produced by an animal could alert producers to mitigate adverse impacts to the herd.
Methane is also a powerful greenhouse gas (GHG) with a GHG potential roughly 25 times that of carbon dioxide. Some scientists estimate that livestock contributes up to thirty-seven percent of the total global methane (CH4) budget. Dairies and beef production operations are therefore identified as a very large global producer of GHGs, with the largest component of their emission footprint resulting from methane production in the rumens of animals. As a consequence, the global CAFO community has made a commitment to reduce the GHG impact resulting from the production of animal products such as meat and milk.
Methane emission from bovine sources, of which the majority is through belching, can be significantly reduced through modification of cattle diet and other management actions. Attempts at methane emission reduction typically involve using nutrient blocks or other feed supplements while other efforts have concentrated on modification of the genetic composition of the animal herd. To date, efforts to measure and potentially remediate this source of GHG from ruminants have not been considered feasible or widely implemented in part because of high costs related to monitoring CH4 emission from ruminants in coordination or concurrently with measurement of supplement use.
Prior to the invention described herein, it has been impractical to actually monitor changes in animal GHG production that result from such efforts. The difficulties and expense of current technology, even for scientists involved in this research, has made it impractical and not cost-effective to make more than a few measurements over relatively short time periods for only a few animals and in only strictly controlled research settings. Therefore, since it is difficult to verify that mitigation plans actually result in decreased methane emissions to the atmosphere, few projects to generate carbon credits or greenhouse gas reduction credits for sale in voluntary markets have been attempted. Likewise, the development of GHG reduction programs for ruminant emissions in the regulated GHG markets of countries has also been inhibited because of the lack of suitable monitoring and verification techniques.
The loss of methane is a significant energy loss to the animal. Globally this is equivalent to trillions of dollars of lost dietary efficiency. Animal nutritionists know that the metabolic pathways in the rumen can be modified by diet to reduce methane production and to more efficiently process feed. Several dietary supplements are available, and, in many cases, the cost of the nutrient supplement is easily exceeded by the animal weight gains, making use of supplements attractive to ruminant producers such as the cattle industry. Accordingly, reduction in methane emissions by ruminants can help animals become more productive per unit of forage or feed while also reducing undesirable methane emissions. When animals eat low quality forage, it actually takes a longer time to pass through their gut. Hence, the poorer the quality of forage, the longer it takes the animals to digest the forage, and this results in lower weight gain but more methane production. However, since monitoring of changes in methane performance under actual field conditions has been difficult or impossible to achieve in the past, it is not practical to modify forage composition to minimize methane losses nor to monitor and modify genetic factors that influence ruminant methane production. A system that can monitor changes in relative methane emissions could therefore provide important information to ruminant producers concerning optimal forage and grazing conditions. In addition, since animals fed a highly energetic diet process that feed more quickly, they produce more methane per unit time, but much less methane per unit of production of meat or milk. Therefore, it can also be important to measure methane and carbon dioxide from the rumen as well as carbon dioxide from the animal's breath in order to differentiate rumen processes from catabolic and respiratory processes and to measure their emissions relative to measurements of animal production, such as animal weight gain and/or animal milk production.
U.S. Pat. No. 5,265,618 discloses a system that measures the flux of metabolic gas emissions from cattle or other animals. The system does not require that the animals be confined to a chamber or stall. An animal whose metabolic gas emissions are to be measured is first fed a permeation tube (i.e., a metal tube with a gas-permeable plastic disk in one end). Inside the tube is a tracer that is physiologically inert. The permeation tube is filled with pressurized liquid tracer, which slowly permeates in gaseous form through the plastic disk. In order to measure rumen-produced and respiratory metabolic gases, a sample container, such as an evacuated container or an inflatable collar, is placed on the animal. A small diameter sample tube is attached from the sample container to a halter and terminates somewhere near the animal's mouth. When the animal breathes, it exhales metabolic gases as well as the tracer. A sample of air containing both the metabolic gases and the tracer gas is then collected through the sample tube. Since the permeation rate of the tracer is known and constant, the ratio of the flux of a given metabolic gas to the flux of the tracer gas is equal to the ratio of the mixing ratios of the respective gases in the air sample that is collected. The rate of flux of metabolic gas from the animal's rumen is thus readily calculated by measuring the metabolic gas and tracer mixing ratios in the sample thus collected. This technique is not well-suited for accurate measurements of carbon dioxide fluxes since background concentrations are relatively high and variable. In addition, this technique is difficult to employ for metabolic gases such as hydrogen sulfide or oxygenated organic compounds that degrade during storage in sample containers. This system also requires substantial animal handling and training to be effective. Moreover, it is not practical for animals that do not tolerate a halter, which may include large percentages of a ruminant herd. Also, the system can only provide time-integrated values that represent average rumen catabolic and respiratory processes. The system cannot be used to track short-term changes nor can it isolate rumen processes from respiratory processes related to catabolism.
Schemes to convert increased ruminant metabolic efficiency into marketable GHG offsets have not been financially viable. Though mineral blocks, other effective nutrient supplements, and rumen-modifying antibiotics and ionophores are effective in reducing methane production and in many cases cost only a few cents per day, at the current value of greenhouse gas (GHG) offsets, compliance, documentation, and monitoring costs exceed the value of the GHG offsets that can be generated. Also, animals fed poor-quality forage have lower methane emission rates per unit time than animals fed high quality diets. However the emission of methane as a function of gross energy intake is much higher for an animal fed low quality forage compared to an animal fed a high quality diet. As a result methane per unit of animal production is much higher for low quality and poorly digested forages compared to animals fed a high quality digestible diet. Specific nutrients, missing from low quality forage can be supplemented through the use of nutrient feeders to boost digestibility, resulting in increased efficiency and lower methane emissions per unit of animal production. It can therefore be desirable to document relative changes in methane emission rates and it may not always be necessary to measure fluxes of methane per unit of time. That is changes in ratios of methane compared to carbon dioxide for respiration as well as for rumen gas per unit of production might provide the information required to document animal performance changes that lead to quantifiable methane reductions and can generate carbon credits. However, measurement of emissions of methane and carbon dioxide from the rumen and differentiation of this flux from measurements of carbon dioxide resulting from catabolism over shorter time periods are necessary in order to track energy flows through a specific ruminant and to document the efficiency of production of meat and milk in a way that facilitates interactive treatment to improve productive efficiency and lower methane emissions per unit of production.